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Problem with Coaxial Piston Valve - New problem on page 2...

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Problem with Coaxial Piston Valve - New problem on page 2...

Unread postAuthor: DaxSF » Wed Oct 19, 2011 5:09 pm

Hi,
New here and working on my 2nd gun (first one had a normal ball valve, YouTube video of the old gun will be on the bottom of the topic).
I have chosen to make a coaxial piston valve to save space and because I think it's the most aesthetic design out there (unless you have milling machines, lathes etc which I don't - only a dremel).

My problem is as you can see in this picture:

Image

There is a piston in the middle part (shiny metal part) and when I pump up the pressure I don't get any equalisation on the chamber - like the piston is completely air tight, but I have made 3 grooves (groove-raged) because I haven't gotten any pressure into the chamber.
When I open the valve on the back all the air goes out of it without opening the piston and allowing any air into the barrel. The piston has a perfect seal on the barrel and it isn't a strong spring.

More pictures:

Image

Video of old gun (if you're interested..):
[youtube]http://www.youtube.com/watch?v=2VXRQEIQ244[/youtube]
Please ignore the titles at the end - as you can see it was made a long time ago.
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Last edited by DaxSF on Wed Oct 19, 2011 8:55 pm, edited 1 time in total.

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Unread postAuthor: Gun Freak » Wed Oct 19, 2011 5:20 pm

I bet it is equilizing, but the grooves and the spring are keeping the valve from piloting. That piston looks way too short to be effective, especially since it is hot glue. I say:
1: take out the spring
2: remake the piston
3. modify the blowgun
And I can guarantee it will work :wink:
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Unread postAuthor: motorfixer1 » Wed Oct 19, 2011 5:27 pm

To me it looks like there is excessive clearance between the O.D. of the piston and the I.D. of the housing. How much travel does the piston have? Why do you have the spring on the barrel side of the piston?
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Unread postAuthor: DaxSF » Wed Oct 19, 2011 5:30 pm

Answering for both questions:
The piston seals perfect, it was longer (1cm longer) and I made it shorter to see if it's equalizing. The barrel is sticking out of the bigger tube so it pushes the piston back a little bit, so the piston is on it's rail, moving smoothly back and forth.
The piston isn't too narrow - it's perfectly fitting inside.

Modify the blowgun - what do you mean by that, what am I suppose to modify?

Thank you both for the VERY fast responces!
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Unread postAuthor: Gun Freak » Wed Oct 19, 2011 5:34 pm

Is it possible for you to upload a picture of the cylinder?
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Unread postAuthor: DaxSF » Wed Oct 19, 2011 5:36 pm

What cylinder?
The chamber which get's air pressurized, the part where the piston slides in or what?

I will upload any picture you ask for, really want to get this gun working lol.
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Unread postAuthor: Gun Freak » Wed Oct 19, 2011 5:59 pm

Yes, the cylinder is where the piston goes.
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Unread postAuthor: jor2daje » Wed Oct 19, 2011 6:30 pm

I dont think you have enough room for the piston to open.
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Unread postAuthor: DaxSF » Wed Oct 19, 2011 6:35 pm

The piston has plenty of room to open, according to Gun Freak's directions (PM's) I am making a new piston because mine was problematic, one without grooves and without a spring.

I'll update back again after I test the new piston.
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Unread postAuthor: Mr.Tallahassee » Wed Oct 19, 2011 6:35 pm

The spring is not on the barrel side. It's on the pilot side, look carefully. I personally don't think the spring is necessary. The air pressure will be more than enough to seat the piston even with a slow fill rate. Don't use such large grooves next time and use some type of lubrication. Lube always makes things much easier and smoother. :wink:
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Unread postAuthor: mattyzip77 » Wed Oct 19, 2011 6:40 pm

Yea, that piston looks mad small! Make a new, longer piston and get rid of the spring, and lube the new piston up with vaseline or something like it. If it still does not work, get rid of that blowgun and try a 1/4 inch ball valve. Good luck, hope you fix it!!
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Unread postAuthor: DaxSF » Wed Oct 19, 2011 7:18 pm

Fixed it :)
Works AMAZINGLY well at only 40-30 PSI I managed to pass through a leather pillow from 5 meters with a 6mm ceramic BB.
All I needed was a bigger piston, no spring and it just worked (you had to see the look on my face when I heard the pop sound of the air going out the barrel for the first time).

BIG BIG thanks to Gun Freak - seriously man, I owe you one.
In a few days I will upload the complete gun with the stock.
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Unread postAuthor: mattyzip77 » Wed Oct 19, 2011 7:20 pm

I still get that same look on my face every time I make a new cannon, congrats, good stuff man!! 8) 8)
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Unread postAuthor: Gun Freak » Wed Oct 19, 2011 7:46 pm

Yay :D
Congratulations :) Glad I could help!
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Unread postAuthor: DaxSF » Wed Oct 19, 2011 8:08 pm

Image

New problem popped up: My blowgun is leaking from the pin part which is pushed to open the valve (Seriously, wtf?).
Anyone got any ideas how to seal it up?.. I can't use any tape because then it wouldn't close or open smoothly, and I can't epoxy it because well.. Then it won't open.
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